Field of the Invention
The invention concerns a method for planning irradiation of a patient for radiation therapy, as well as an irradiation planning computer and a non-transitory, computer-readable data storage medium encoded with programming instructions for implementing such a method.
Description of the Prior Art
In radiation therapy, target tissue, for example a tumor, of a patient is irradiated with ionizing radiation. External radiation therapy, wherein irradiation of the body of the patient originates from outside of the body, is known in this connection. Internal radiation therapy, also called brachytherapy, is likewise known. In brachytherapy, radiation sources, which include radioactive substances, are introduced into the body of the patient to locally damage or destroy target tissue in the body of the patient.
It is known to plan and/or monitor irradiation of a patient with the use of imaging. An irradiation plan is conventionally created for this purpose with the use of medical scan data of the patient, created using a three-dimensional imaging method. Computed tomography scan data (CT scan data) are conventionally used for this purpose. Using the CT scan data, firstly the target volume of the irradiation can be defined, and, secondly, surrounding tissue that is to be spared—for example nerve tissue—is localized. Furthermore, the intensity values of the image voxels of the scan data (measured in what are known as “Hounsfield Units”) map an electron density at the corresponding location in the body of the patient in a good approximation since the intensity values of the image voxels are based on absorption of the X-ray radiation at the associated locations. In this way the CT scan data can be converted particularly easily into an electron density map for irradiation planning. Since the intensity of the interaction of the radiation correlates with the electron density in the body in the case of irradiation, the attenuation of the radiation as it passes through the body can be calculated easily from the CT scan data. It is due to this property that previously CT scan data has preferably been used when creating an irradiation plan.
However, there is a need to use other imaging methods in irradiation planning that have better soft tissue contrast in order to enable improved identification of target organs and/or organs at risk. One imaging method of this kind, which satisfies the requirement for better soft tissue contrast, is magnetic resonance imaging (MR imaging) by the use of a magnetic resonance device. With imaging of this kind the contrast depends on the distribution of the spin density, the interaction of the spins among each other and/or with their surroundings. A soft tissue contrast can be achieved with MR imaging that is significantly superior to the contrast that can be achieved with a computed tomography device. Furthermore, functional contrasts, for example a diffusion contrast, can also be advantageously recorded with magnetic resonance imaging for irradiation planning.